Scanning mirrors are useful in a variety of applications. Scanning mirrors may be used in scanning or projection devices to enable detection of light from a range of directions, or to enable projection of light into a range of directions.
In telecommunications, scanning mirrors may be useful in creation or maintenance of an optical communications link (“optical WiFi”). Such an optical communications link may enable wireless communications with increased privacy as compared with radio-based communications. For example, a static transceiver link device may be mounted at a fixed position, such as in a ceiling or wall. A moveable communication device (e.g., desktop or laptop computer, or other device with communications capability) is provided with a similar transceiver port (or attached device).
The moveable communication device may be placed within a region toward which a beam of the static transceiver link is aimed. However, in the absence of scanning capability, the moveable communication device would have to be placed sufficiently accurately so that the transceiver port of the moveable communication device is accurately aligned with the static transceiver link. Such accurate placement of the moveable communication device could be difficult or frustrating for many users. Furthermore, the moveable communication device may be intentionally or unintentionally moved during use and that would cause communication disruption.
However, equipping the static transceiver link, the moveable communication device, or both with scanning mirrors may enable creation and maintenance of the link. For example, the mirrors may be scanned (e.g., in a predetermined pattern) to change a direction of a transmitted beam or of a field of view of a detector until an optical communication link is established or restored. The mirror may be scanned in accordance with detected motion in order to maintain the optical communication link.
A mechanism useful for scanning the mirror may depend on various properties of the mirror, or on other factors. For example, in microelectromechanical systems (MEMS) technology (e.g., sub-millimeter sized mirrors), piezoelectric devices or materials (e.g., lead zirconate titanate—PZT) may be used to tilt the mirror. Control of such devices may be complex. Similarly, electrostatic forces may be applied to tilt such MEMS mirrors. However, electrostatic forces are typically much weaker (e.g., by a factor on the order of about one million) than the forces applied by piezoelectric devices. Scanning of larger mirrors may be effected by use of motors or similar devices.
The strength of electrostatic fields that are created to tilt a mirror may be limited by various constraints. For example, electrical fields in air may be limited by electrical breakdown considerations to below the dielectric strength of air. If the mirror tilts sufficiently such that a part of the mirror approaches an electrode, the mirror may continue to tilt in an unrestrained manner an edge of the mirror comes into contact with and sticks to the electrode.